Some movies are time capsules. Take the lid from this can of film and you can inhale pure essence of 1974. Whether this makes for a great documentary is open to debate: maybe A Poem Is a Naked Person is of purely archival interest. It is Les Blank’s boldly experimental, very indulgent film from 1974 about the country-rocker Leon Russell; a film withheld for decades owing to disagreements between film-maker and subject, and inevitable wrangles about music rights; it only reached the public after Blank’s death in 2013.

It is a kind of self-deconstructing documentary. Despite conventional footage of interviews and concerts, it moves away from Russell to something else, somewhere else, to scenes and images that are beside the point. But that is the point. It free-associates its way towards loose, garrulous, outrageously irrelevant sequences concerning people who happen to exist in Oklahoma at the same time as Russell. Sometimes it’s inspired … and sometimes it’s as if a documentary about Russell has been interrupted by a very, very dull edition of the local TV news.